This invention relates to a lighting apparatus, and particularly to a task lighting apparatus which illuminates surface such as the work surface of an office desk.
In conventional device, reflector at the back of light source, for example, straight tube fluorescent lamp is provided to illuminate surface to be illuminated, for example, the ceiling board (work surface) of an office desk in almost even illumination. The beam emitted from the fluorescent lamp is turned by the reflector to the region of the ceiling board near the person at desk. This improves the distribution of illuminance in the region of the ceiling board corresponding to the region near the hands of the person at desk. However, the light emitted from the task lighting apparatus reflects diametrically in the region of the ceiling board situated in front of the person at desk to produce undesirable reflection, so-called veiling reflection.
In order to prevent this veiling reflection, a task lighting apparatus as illustrated in FIGS. 1 to 3 has been developed. A light source, for example, straight tube fluorescent lamp 10 is provided on the ceiling board (work surface) 12 of the office desk 14 as shown in FIG. 1. This fluorescent lamp 10 is held in a housing 16. This housing 16 is fixed to the office desk 14 by means of the support members 18. This housing 16 has at least one opening at its lower position. This opening is provided with a light-transmitting plate 20 shown in FIG. 2. A plurality of V-shape grooves 22 are formed on the face where this light-transmitting plate is opposite to the fluorescent lamp 10. These V-shape grooves 22 are provided in the direction of the tube axis of the fluorescent lamp 10 and are in parallel with one another. When the light emitted from the light source 10 of the fluorescent lamp falls on the light-transmitting plate 20, it is split to two directions shown by the arrows 24, 26, respectively. That is, the V-shape grooves 22 formed on the light-transmitting plate 20 functions as prisms. Therefore, the beam illuminating the work surface 12 of the office desk 14, as shown in FIG. 1, radiates in the directions 24, 26 on the plane almost perpendicular to the work surface 12 and including the tube axis of the straight tube fluorescent lamp 10. In other words, so-called twin beam distribution is formed. As a result, the above-mentioned veiling reflection can be prevented. However, this has a disadvantage that only the region just under the lighting device of the work surface 12 is illuminated in brightness but the whole work surface is not evenly illuminated. Further, this has another disadvantage that the fatigue of the eyes of the person at desk is undesirably on the increase, because the region of the work surface on the side of the hand of the person at desk gets dark.